Experience-hormone interactions and maternal behavior in rats

Abstract

Three studies were conducted to determine the effects of reproductive condition and hormonal background on the acquisition and retention of a prior maternal experience. In the first study five experience conditions were compared. All animals gave birth and received either no postpartum contact with pups or 1 2 hr, 1 hr, 2 hr or 24 hr of pup contact and were tested for maternal behavior 10 days later. Animals receiving pregnancy and parturitional experience, but minimal social experience with young, exhibited significantly longer maternal onset latencies than did groups receiving 2 or 24 hr of prior experience; also, comparisons of 10- and 30-day retention intervals indicated that animals tested 10 days after a 24-hr experience exhibited shorter latencies than those tested 30 days later. Thus, the duration of the postpartum experience and the interval since prior experience both affect the level of maternal responsiveness shown. In the second study six groups of females were tested. Four groups were permitted one day of interaction with pups either after parturition (primiparous animals) or following pup induction procedures (nulliparous animals) and were tested for their maternal responsiveness to foster pups 25–35 days later, either on day 19 of a subsequent pregnancy or following resumption of estrous cycling. For most measures of maternal behavior there were significant main experience and test effects; experienced and pregnant animals exhibited shorter latencies to retrieve, lick and crouch over pups than did inexperienced and cycling animals, respectively. Significant interactions were also found for genital licking latency as well as for retrieval and crouch frequencies. Primiparous experienced females tested during pregnancy exhibited higher levels of these behaviors than any other group. In the third study four groups of ovariectomized nulliparous animals were primed with the “maternal” hormones, progesterone and estradiol, and were given either 1 day of maternal experience following pup induction of maternal behavior or no experience. Animals were tested for maternal behavior 23–35 days later either following priming with progesterone and estradiol or following control injections. Consistent with the second study, the group exhibiting the shortest maternal onset latency was the maternally experienced group tested under hormonal priming. These data indicate that maternal experiences are more persistent if they are obtained under hormonal priming and are more easily activated if tests occur under hormonal priming; for many of the measures the effects of the two conditions are additive. Ways in which hormones might act to promote these effects are discussed.